The file "COMPATIBILITY" from the ksh93 source might help you to
adjust the scripts if you like,

Extract:
 "[...] a list of known incompatibilities between ksh-93 and ksh-88.
  I have not include cases that are clearly bugs in ksh-88.  I also have
  omitted features that are completely upward compatible."

If you want to glance at it, search for "ksh-93 vs. ksh-88" in
<URL:http://uw7doc.sco.com/DIFFS/UNIX95_Conformance.html>

There are more details in the files RELEASE88/93.

(AFAIK you'll be having a hard time to get ksh88 source.)
(Tried the latest version of pdksh?)

Sven